SMJ320C25, SMJ320C2550

DIGITAL SIGNAL PROCESSOR

SGUS007D – AUGUST 1988 – REVISED OCTOBER 2001

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POST OFFICE BOX 1443

16 X 16-bit parallel multiplier (continued)

Four product shift modes are available at the product register (PR) output that are useful when performing

multiply/accumulate operations, fractional arithmetic, or justifying fractional products.

timer

The SMJ320C25 provides a memory-mapped 16-bit timer for control operations. The on-chip timer (TIM)

register is a down counter that is continuously clocked by CLKOUT1. A timer interrupt (TINT) is generated every

time the timer decrements to zero. The timer is reloaded with the value contained in the period (PRD) register

within the next cycle after it reaches zero so that interrupts can be programmed to occur at regular intervals of

PRD + 1 cycles of CLKOUT1.

memory control

The SMJ320C25 provides a total of 544 16-bit words of on-chip data RAM, divided into three separate blocks

(B0, B1, and B2). Of the 544 words, 288 words (blocks B1 and B2) are always data memory, and 256 words

(block B0) are programmable as either data or program memory. A data memory size of 544 words allows the

SMJ320C25 to handle a data array of 512 words (256 words if on-chip RAM is used for program memory), while

still leaving 32 locations for intermediate storage. When using block B0 as program memory, instructions can

be downloaded from external program memory into on-chip RAM and then executed.

When using on-chip program RAM, ROM, or high-speed external program memory, the SMJ320C25 runs at

full speed without wait states. However, the READY line can be used to interface the SMJ320C25 to slower,

less-expensive external memory. Downloading programs from slow off-chip memory to on-chip program RAM

speeds processing while cutting system costs.

The SMJ320C25 provides three separate address states for program memory, data memory, and I/O. The

on-chip memory is mapped into either the 64K-word data memory or program memory space, depending upon

the memory configuration. The CNF0 (configure block B0 as data memory) and CNFP (configure block B0 as

program memory) instruction allow dynamic configuration of the memory maps through software. Regardless

of the configuration, the user can still execute from external program memory.

The SMJ320C25 has six registers which are mapped into the data memory space: a serial port data receive

register, serial port data transmit register, timer register, period register, interrupt mask register, and global

memory allocation register.